1. Field of the Invention
This invention relates to systems for transmitting gas, particularly natural gas, under pressure throughout a transmission and distribution network, and, more particularly, to an improved method for cooling the gas after its compression and before its transmission to the next leg of the transmission-distribution network.
2. Prior Art
In a transmission system for heating and illuminating gas, such as natural gas, in order to distribute the gas efficiently it is necessary that it be compressed. As is well known, when a gas is compressed, a great deal of heat is generated and, before the gas can be distributed efficiently, it must be cooled, say from 150.degree. F. to 90.degree. F. This cooling step is performed in a cooling tower in which there are fans which are driven through drive-belts from electrical motors, one for each fan. For example, a tower may have 12 fans each 12 feet in diameter and rotating at 268 rpm. In prior art systems, when the requirement for cooling was such that only a portion of the total cooling capacity was required, one or more of the fans in the cooling tower were turned off by switching off the drive-motor associated with each of those fans. Thus, no power was transmitted from the respective electrical motor through its associated drive-belt to the subject fan and the induced draft from the remaining operating fans could cause the idle fans to "windmill" in a direction opposite to that in which they would rotate when driven by their associated electrical motors. Under these conditions, difficulties frequently arose when the motors coupled to the previously idle fans were turned on. For example, the belts between the drive-motors and the sheaves or pulleys on the shafts associated with the fans would jump out of those sheaves or pulleys with the sudden attempt to rotate them in a direction opposite to that in which they were "windmilling". Further, the drive motors had a tendency to draw excessive electrical current during any such sudden attempt to reverse the direction of rotation of the fan blades and there was a corresponding opening of the associated circuit breakers, which then required attention from maintenance personnel. Thrown belts were also experienced and required attention from maintenance personnel.
Therefore, it is a first object of this invention to overcome the various problems recited hereinbefore.
It is a further object of this invention to provide a gas transmission and distribution system and associated apparatus which will cause the cooling fans in the system to rotate in a single direction determined by the drive motor associated with each of the fans.